In healthy young subjects, training increases insulin sensitivity but decreases the capacity to secrete insulin. We studied whether training changes β-cell function in type 2 diabetic patients. Patients, stratified into “moderate” and “low” secretors according to individual C-peptide responses to an intravenous glucagon test, were randomly assigned to a training program [ergometer cycling 30–40 min/day, including at least 20 min at 75% maximum oxygen consumption (V̇o2 max), 5 days/wk for 3 mo] or a sedentary schedule. Before and after the intervention (16 h after last training bout), a sequential hyperglycemic (90 min at 11, 18, and 25 mM) clamp was performed. An intravenous bolus of 5 g of arginine was given at the end. Training increased V̇o2 max 17 ± 13% and decreased heart rate during submaximal exercise ( P < 0.05). During the 3 mo of sedentary lifestyle, insulin and C-peptide responses to the clamp procedures were unchanged in both moderate and low secretors. Likewise, no change in β-cell response was seen after training in the low secretors ( n = 5). In contrast, moderate secretors ( n = 9) showed significant increases in β-cell responses to 18 and 25 mM hyperglycemia and to arginine stimulation. Glucagon responses to arginine as well as measures of insulin sensitivity and Hb A1c levels were not altered by training. In conclusion, in type 2 diabetic patients, training may enhance β-cell function if the remaining secretory capacity is moderate but not if it is low. The improved β-cell function does not require changes in insulin sensitivity and Hb A1c concentration.
Improved <i>β</i>-cell function rather than increased insulin sensitivity is associated with reduction in hemoglobin A1c in newly diagnosed Type 2 diabetic patients treated with metformin
